The present invention relates to the field of systems for drawing fuel from a motor vehicle tank.
Numerous systems have been proposed for this purpose.
In general, systems for drawing fuel from a motor vehicle tank comprise an electric pump which sucks in fuel from the tank or from a reserve situated in the tank.
The purpose of such a reserve is to limit variations in fuel level at the inlet of the pump, as can result from accelerations, decelerations, or centrifugal forces when the vehicle is traveling along a curved path.
Furthermore, known drawing systems generally comprise a coarse filter or strainer placed at the pump inlet, and a fine filter for guaranteeing the quality of the fuel that is sent to the engine.
Proposals have been made in particular for fuel-drawing systems in which the fine filter is situated downstream from the electric pump, e.g. as described in document WO-A-99/01658.
Known drawing systems have already given good service.
However, they do not give full satisfaction.
In particular, in spite of a great deal of research, it has not yet been possible to provide a proper solution to the various requirements for development that make themselves felt in the automotive industry.
Firstly, it should be observed that when the fine filter is situated downstream from the pump, i.e. on its outlet duct, the fine filter is placed under pressure so its housing must present mechanical strength suitable for being stressed by said pressure.
That has led to a desire for the fine filter to be located not downstream from the pump but upstream therefrom, e.g. at its inlet. That would enable stresses on the housing for the fine filter to be reduced and, in some cases, might even make it possible to omit the inlet strainer.
However, placing the fine filter upstream from the pump gives rise to a problem that has not yet been solved in satisfactory manner: when the system is first started, or after it has lost priming, or when fuel levels are low, if the fine filter is situated upstream from the pump, then the electric pump must also suck in a large volume of air corresponding substantially to the volume of the housing for the fine filter.
Secondly, it should be observed that until now most electric pumps used in fuel-drawing systems are of the rotary gear pump type. Such pumps operate on the principle of sucking liquid into the space that lies between two consecutive teeth and in then causing the liquid to travel into a delivery section.
However, at present, there is strong demand for rotary gear pumps to be replaced by turbine or centrifugal pumps since they present genuine advantages. Turbine or centrifugal pumps are machines in which rotation of a wheel or rotor produces pressure and speed conditions which cause a liquid to flow in a circuit, with the magnitude of the flow rate being the result of equilibrium between the working energy per unit mass delivered by the pump and the resistive energy per unit mass of the circuit.
Nevertheless, at present, in numerous configurations, attempts at using turbine pumps or centrifugal pumps for drawing fuel have not given satisfaction because of the priming problems that are inherent to pumps of those types. This problem is particularly acute for systems in which the fine filter is situated upstream from the pump because of the head loss that the filter generates.
Thirdly, it should be emphasized that turbine pumps or centrifugal pumps generally possess a degassing orifice. The presence of such a degassing orifice through the casing of the pump leads to a risk, when the pump is not in operation, not only of contaminating the pump""s own internal volume, but also of contaminating at least a portion of the volume of the housing for the fine filter connected thereto.
Fourthly, it should be emphasized that the presence of the degassing orifice in the casing of the pump can lead to a risk of the positive reserve associated with the pump being emptied via said degassing orifice, unless special precautions are taken.
An object of the present invention is to improve known fuel-drawing systems in order to eliminate the above-mentioned drawbacks inherent to the prior art.
In the context of the present invention, this object is achieved by a device for drawing fuel for a motor vehicle tank, the device comprising a drawing pump and a fine filter placed upstream from the pump, and being characterized by the facts that:
the housing of the filter possesses a degassing orifice in the top portion thereof;
the drawing pump also possesses a degassing orifice; and
the filter housing is fitted with a duct which extends the degassing orifice of the housing, opens out into a cavity common to the degassing orifice of the pump, and possesses a mouth situated at a height that is equal to or lower than that of the degassing orifice of the pump, said duct being shaped so as to constitute a siphon suitable for conveying fuel around the mouth to the inside of the filter housing while the drawing pump is being stopped.
According to an advantageous characteristic of the present invention, the inlet chamber of the filter housing is fed and pressurized by means of a jet pump, thus making it possible to pressurize the inlet stage of the filter so as to assist the pump in its suction process.